Information
-
Patent Grant
-
6247416
-
Patent Number
6,247,416
-
Date Filed
Friday, March 26, 199925 years ago
-
Date Issued
Tuesday, June 19, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Ferensic; Denise L.
- Rinehart; K. B.
-
CPC
-
US Classifications
Field of Search
US
- 110 185
- 110 186
- 110 188
- 110 190
- 431 68
- 236 15
-
International Classifications
-
Abstract
The invention relates to a method of operating a furnace (1) comprising a flue pipe (11) for discharging the smoke, means (19) of introducing ambient air into the said flue pipe (11) and a smoke extractor (16) arranged in the said flue pipe (11). According to the method, the temperature of the smoke is measured at two points (31, 33), the temperature measured at the second point (33) is subtracted from the one measured at the first point (31), the result of the subtraction is compared with a datum value ΔT, and the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace (1) is decreased when the result of the subtraction is below the datum value ΔT.
Description
This application claims priority under 35 U.S.C. §§119 and/or 365 to 98 04115 filed in France on Apr. 2, 1998; the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of operating a furnace such as, for example, a rotary oxycombustion furnace, comprising an elbowed flue pipe for discharging the smoke at the furnace outlet, means of introducing ambient air into the said flue pipe and a smoke extractor arranged in the flue pipe, downstream of the said means of introducing ambient air.
2. Description of the Related Art
Methods of running such a furnace are known, and in these methods, in a first step, a gas analyser is used to analyse the, for example, CO content of the smoke and, in a second stage, the amounts of fuel and of oxidizing agent introduced into the furnace are adjusted as a function of the measurement result obtained.
These methods of operating a furnace using a gas analyser have the drawback of being expensive and complex.
This is because gas analysers are technologically advanced measurement instruments which are therefore very expensive, especially where highly reliable and very accurate analysers are concerned.
Furthermore, because of the construction and operation of a gas analyser, the measurement results it yields drift over time, which means that the analyser requires regular calibration.
Added to this is the fact that this gas analyser requires the attention of a specially qualified operator to maintain this measurement instrument and keep it operating correctly.
The invention sets out to alleviate these various drawbacks by proposing a method of operating a furnace and a device for implementing this method which is reliable and of low cost.
SUMMARY OF THE INVENTION
To this end, the subject of the invention is a method of operating a furnace comprising a flue pipe for discharging the smoke, means of introducing ambient air into the said flue pipe and a smoke extractor arranged in the said flue pipe, downstream of the said means of introducing ambient air, characterized in that:
the temperature of the smoke is measured at two points, one of which is close to the outlet of the furnace, and the other of which is in the flue pipe, downstream of the first point,
the temperature measured at the second point is subtracted from the one measured at the first point,
the result of the subtraction is compared with a positive or zero datum value ΔT, and
the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace is decreased when the result of the subtraction is below the datum value ΔT.
The method according to the invention may additionally comprise one or more of the following features:
the datum value ΔT corresponds to the difference between the temperature of the smoke at the first point and that at the second point when the furnace is running optimally,
the datum value ΔT is equal to zero,
after the said reduction, the temperature measured at the first point is also compared with a reference temperature and the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace is increased when the temperature of the smoke measured at the first point is below the reference temperature.
Another subject of the invention is a device for operating a furnace comprising a flue pipe for discharging the smoke, means of introducing ambient air into the said flue pipe and a smoke extractor arranged downstream of the said means of introducing ambient air, for implementing the method as defined hereinabove, characterized in that it further comprises a first and a second sensor for measuring the smoke temperature, the first of which is placed close to the outlet of the furnace, and the second of which is placed in the flue pipe, downstream of the first sensor, means of subtracting the temperature measured by the second sensor from the one measured by the first sensor, means of comparing the result of the subtraction with a datum value ΔT and, controlled by the said comparison means, means of reducing the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace when the result of the subtraction is below a datum value.
The device according to the invention may additionally comprise the feature whereby it additionally comprises means of storing a reference temperature, means of comparing the temperature measured by the first sensor with the reference temperature and, controlled by the said means of comparing the temperature measured by the first sensor with the reference temperature, means of increasing the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace when the smoke temperature measured by the first sensor is below the reference temperature.
BRIEF DESCRIPTION OF THE FIGURE OF THE DRAWING
Other features and advantages of the invention will emerge from the following description, given by way of non-limiting example, with reference to the appended drawing which depicts a diagram of an oxycombustion rotary furnace equipped with a device according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The single figure depicts an oxycombustion rotary furnace
1
equipped with an operating device
3
according to the invention.
The furnace
1
comprises an inlet
5
which has a burner
7
via which an oxidizing agent such as, for example, oxygen or oxygen-enriched air, and a fuel, for example natural gas, are introduced into the furnace
1
, and an outlet
9
via which the smoke, that is to say the products of combustion, are discharged towards a flue pipe
11
.
The flue pipe
11
comprises an elbowed portion
13
which is extended by a vertical portion
14
in which a filter
15
followed by an extractor
16
are arranged.
The extractor
16
sucks the smoke leaving the furnace
1
into the flue pipe
11
and ejects this smoke, once filtered, out into the surrounding atmosphere.
In order to be able to withstand the high temperature of the smoke leaving the furnace, the internal walls of the elbowed portion
13
are lined with a refractory material
17
.
Furthermore, the inlet
18
of the elbowed portion
13
has a shape which widens towards the outlet
9
of the furnace
1
and is arranged facing it from a distance, with a certain gap
19
in between.
The gap
19
between the inlet
18
of the flue pipe
11
and the outlet
9
of the furnace
1
acts as a means of introducing ambient air into the flue pipe
11
to cool the smoke leaving the furnace
1
before this smoke reaches the filter
15
arranged further downstream.
The device
3
for operating the furnace
1
comprises a first temperature sensor
30
arranged at a first point
31
close to the outlet
9
of the furnace, that is to say either directly in this outlet or, as has been depicted in the drawing, just at the inlet
18
of the elbowed portion
13
of the flue pipe
11
. As a preference, the sensor
30
is centred in the inlet
18
so that it does not come into contact with the ambient air (indicated by arrows
25
) which enters the flue pipe
11
from the side under the effect of the suction of the extractor
16
.
The device
3
for operating the furnace
1
additionally comprises a second temperature sensor
32
arranged at a second point
33
centred in the flue pipe
11
downstream of the first point
31
, preferably after the elbowed part
13
of the flue pipe
11
.
The temperature sensors
30
and
32
consist for example of thermocouples.
Each sensor
30
,
32
is connected to one input of a subtractor
34
, whose result—the subtraction of the temperatures delivered by the sensors
30
and
32
—is compared in a first comparator
35
with a positive or zero datum value ΔT stored in a memory
35
A. As a preference, the datum value ΔT is a value determined experimentally and which corresponds to the difference in temperatures at the first point
31
and at the second point
33
, respectively, when the furnace is at optimal settings. In this context, it is considered that the furnace is at optimal settings when its efficiency is at a maximum, which occurs when, on the one hand, there is no excess of oxygen cooling the furnace and, on the other hand, the CO content in the smoke leaving the furnace is at a minimum. However, this datum value may also be equal to zero in a simplified embodiment of the invention. Depending on the result of the comparison, the comparator
35
controls the means
36
of regulating the flow rates of oxidizing agent and of fuel introduced into the furnace
1
via a line
38
for controlling the flow rate of oxidizing agent and a line
40
for controlling the flow rate of fuel, both connected to the burner
7
.
Incidentally, the device
3
comprises a second comparator
42
, a first input of which is connected to the sensor
30
and a second input of which is connected to means
44
of storing a reference temperature. The output of the second comparator
42
is also connected to the regulating means
36
so as to control these as a function of the result of the comparison between the temperature delivered by the sensor
30
and the reference temperature stored in the memory
44
.
The running of the method for operating the furnace
1
according to the invention and the operation of the device
3
for implementing this method, are described hereafter.
When the furnace
1
is in operation, a certain oxidizing agent/fuel mixture is introduced into the furnace
1
via the burner
7
, this mixture being regulated by the means
36
of regulating the flow rates. This mixture may be characterized by the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace
1
.
Apart from when the furnace is operating at optimal settings, there are, in particular, two reduced-efficiency modes of operation of the furnace that can be considered.
Firstly, when the mixture introduced into the furnace
1
has an excess of fuel, there is not enough oxygen to be able to burn all of the fuel introduced into the furnace
1
, which means that the CO content of the smoke increases. The smoke sucked into the flue pipe
11
mixes with the ambient air introduced. Because of the high temperature of the smoke and the presence of the oxygen in the air, the CO burns in a region
50
known as the post-combustion region, and this causes the temperature of the smoke in the portion
13
to rise to a higher level, particularly a level that is higher than that of the smoke leaving the furnace
1
.
Secondly, when the oxidizing agent/fuel mixture introduced into the furnace
1
has too great an amount of oxidizing agent, the furnace becomes cooled which, for example in the case of a smelting furnace, increases the smelting time and thus the running cost of the installation.
To correct the excess fuel, the method according to the invention consists in measuring, on the one hand, by means of the sensor
30
, the temperature of the smoke leaving the furnace
1
, and on the other hand, downstream of the sensor
30
and using the sensor
32
, the temperature of the smoke downstream of the region
50
in which post combustion may occur. The temperature measured by the sensor
32
is subtracted from the one measured by the sensor
30
using the subtractor
34
. The result of the subtraction is compared with the datum value ΔT in the device
3
using the comparator
35
.
If the result of the subtraction is below the datum value ΔT, or even negative, which means that post combustion has taken place between the two points where the temperature is measured because of a high CO content in the smoke leaving the furnace
1
and as a result of an excess of fuel, the comparator
35
commands a reduction in the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace by means
36
. This reduction in the ratio between the two flow rates can be achieved either by increasing the flow rate of oxidizing agent or by decreasing the flow rate of fuel introduced into the furnace.
So, to avoid excess oxidizing agent, the temperature measured by the sensor
30
is also compared with the reference temperature stored in the memory
44
. This reference temperature is a temperature value found by experimentation and which corresponds to the temperature of the smoke leaving the furnace when the latter is operating at optimal settings.
If the comparison by the comparator
42
reveals that the temperature measured by the sensor
30
is below the reference temperature, which means that an excess of oxidizing agent has been introduced into the furnace
1
, the comparator
42
commands the means
36
to increase the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace, and this is achieved either by reducing the flow rate of oxidizing agent or by increasing the flow rate of fuel.
In order to confine the furnace to a certain operating range, it is also possible within the regulating means
36
to define minimum and maximum flow rates for the oxidizing agent and for the fuel.
It can therefore be seen that the method according to the invention and the device for implementing it require only a relatively low investment. Furthermore, the hardware used, particularly the thermocouples, has the advantage of being robust and easy to install and maintain.
Claims
- 1. Method of operating a furnace (1) comprising a flue pipe (11) for discharging the smoke, means (19) of introducing ambient air into the said flue pipe (11) and a smoke extractor (16) arranged in the said flue pipe (11), downstream of the said means (19) of introducing ambient air, characterized in thatthe temperature of the smoke is measured at two points (31, 33), one (31) of which is close to the outlet (9) of the furnace (1), and the other (33) of which is in the flue pipe (11), downstream of the first point (31), the temperature measured at the second point (33) is subtracted from the one measured at the first point (31), the result of the subtraction is compared with a positive or zero datum value ΔT, and the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace (1) is decreased when the result of the subtraction is below a datum value ΔT and wherein the temperature measured at the first point (31) is also compared with a reference temperature and in that the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace (1) is increased when the temperature of the smoke measured at the first point (31) is below the reference temperature.
- 2. Method according to claim 1, characterized in that the datum value ΔT corresponds to the difference between the temperature of the smoke at the first point (31) and that at the second point (33) when the furnace is running optimally.
- 3. Method according to claim 1, characterized in that the datum value ΔT is equal to zero.
- 4. Device for operating a furnace comprising a flue pipe for discharging the smoke, means (19) of introducing ambient air into the said flue pipe (11) and a smoke extractor (16) arranged downstream of the said means (19) of introducing ambient air, for implementing the method according to claim 1, characterized in that it further comprises a first and a second sensor (30, 32) for measuring the smoke temperature, the first (30) of which is placed close to the outlet (9) of the furnace, and the second (32) of which is placed in the flue pipe (11), downstream of the first sensor (30), means (34) of subtracting the temperature measured by the second sensor (32) from the one measured by the first sensor (30), means (35) of comparing the result of the subtraction with a datum value ΔT and, controlled by the said comparison means (35), means (36) of reducing the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace (1) when the result of the subtraction is below a datum value.
- 5. Device for operating a furnace (1) according to claim 4, characterized in that it additionally comprises means (44) of storing a reference temperature, means (42) of comparing the temperature measured by the first sensor (30) with the reference temperature and, controlled by the said means (42) of comparing the temperature measured by the first sensor (30) with the reference temperature, means (36) of increasing the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace (1) when the smoke temperature measured by the first sensor (30) is below the reference temperature.
- 6. Method according to claim 2, characterized in that after the said reduction, the temperature measured at the first point (31) is also compared with a reference temperature and in that the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace (1) is increased when the temperature of the smoke measured at the first point (31) is below the reference temperature.
- 7. Method according to claim 3, characterized in that after decreasing the ratio of the flow rate of fuel to the flow rate of the oxidizing agent, the temperature measured at the first point (31) is also compared with a reference temperature and in that the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace (1) is increased when the temperature of the smoke measured at the first point (31) is below the reference temperature.
- 8. Device for operating a furnace comprising a flue pipe for discharging the smoke, means (19) of introducing ambient air into the said flue pipe (11) and a smoke extractor (16) arranged downstream of the said means (19) of introducing ambient air, for implementing the method according to claim 2, characterized in that it further comprises a first and a second sensor (30, 32) for measuring the smoke temperature, the first (30) of which is placed close to the outlet (9) of the furnace, and the second (32) of which is placed in the flue pipe (11), downstream of the first sensor (30), means (34) of subtracting the temperature measured by the second sensor (32) from the one measured by the first sensor (30), means (35) of comparing the result of the subtraction with a datum value ΔT and, controlled by the said comparison means (35), means (36) of reducing the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace (1) when the result of the subtraction is below a datum value.
- 9. Device for operating a furnace comprising a flue pipe for discharging the smoke, means (19) of introducing ambient air into the said flue pipe (11) and a smoke extractor (16) arranged downstream of the said means (19) of introducing ambient air, for implementing the method according to claim 3, characterized in that it further comprises a first and a second sensor (30, 32) for measuring the smoke temperature, the first (30) of which is placed close to the outlet (9) of the furnace, and the second (32) of which is placed in the flue pipe (11), downstream of the first sensor (30), means (34) of subtracting the temperature measured by the second sensor (32) from the one measured by the first sensor (30), means (35) of comparing the result of the subtraction with a datum value ΔT and, controlled by the said comparison means (35), means (36) of reducing the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace (1) when the result of the subtraction is below a datum value.
- 10. Device for operating a furnace comprising a flue pipe for discharging the smoke, means (19) of introducing ambient air into the said flue pipe (11) and a smoke extractor (16) arranged downstream of the said means (19) of introducing ambient air, for implementing the method according to claim 1, characterized in that it further comprises a first and a second sensor (30, 32) for measuring the smoke temperature, the first (30) of which is placed close to the outlet (9) of the furnace, and the second (32) of which is placed in the flue pipe (11), downstream of the first sensor (30), means (34) of subtracting the temperature measured by the second sensor (32) from the one measured by the first sensor (30), means (35) of comparing the result of the subtraction with a datum value ΔT and, controlled by the said comparison means (35), means (36) of reducing the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace (1) when the result of the subtraction is below a datum value, and also comprises means (44) of storing a reference temperature, means (42) of comparing the temperature measured by the first sensor (30) with the reference temperature and, controlled by the said means (42) of comparing the temperature measured by the first sensor (30) with the reference temperature, means (36) of increasing the ratio of the flow rate of fuel to the flow rate of oxidizing agent introduced into the furnace (1) when the smoke temperature measured by the first sensor (30) is below the reference temperature.
Priority Claims (1)
Number |
Date |
Country |
Kind |
98 04115 |
Apr 1998 |
FR |
|
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|
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|
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